Railway traffic controlling apparatus



` Aug. 10, 1943. AFQ, K CRC-@Ks 2,326,522

RAILWAY TRAFFJ-.C CONTROLLING APPARATUS Filed Feb. 13, i942 la Ib Patented Aug. 10, 1943 RAILWAY TRAFFIC coN'moLLING APPARATUS Ralph Crooks, Sharpsburg, Pa., assignor to The Union Switch `t Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 13, 1942,*Serial No.7430,776 6 alarma (01.7246-63) My invention relates to railwayftrafic controlling apparatus, and more'particularly to train carried train control apparatus responsive to coded energy. i Y x Train carried train control apparatus responsive to coded alternating current often includes in the receiving circuit a filter tuned to resonance at the frequency of the alternating current with the result that the oscillations that persist after the current isinterrupted at the end of each on code period may create code distortion when the magnitude of the rail current becomes relatively large as may be the case when the train is close to the exit end of a track section and the rail impedance is shunted out. Rail current of such large magnitude so excites the filter'that its oscillatory condition tends to fill in the valleys (off periods) of the envelope of the received electromotiveforce. Again,.it has been proposed to use amplifier tubes operative from the usual 32 volt train carriedgenerator or battery Without voltage converters. Variations in the amplification factor of such tubes due to the voltage variations of such current source may cause over and under excitation of the usual code following relay governed by the amplifier, If the energization of the relay exceeds its predetermined value any one on code period, the operation of the relay at the next off code period is delayed due tothe longer time for the 'energization to die down to the operating value of the relay and code distortion results. Under-energization of the relay may likewise cause code distortion and of course may cause failure of the relay to operate. Hence the amplifier gain must be controlled if uniform energization of the code following relay is to be assured over the usual range of voltages of the train carried source and also if over-energization due to the oscillatory condition of thereceiving circuit is minimized.

Another feature of my invention is the provision of train carried train control apparatus incczporating a novel electron tube amplifier requiring but a single 32 volt source of direct curv rent and energy from the usual 32 volt train carried generator can. be used Without voltage conver ers, and which amplifier provides inverse feed-back to compensate for the changes in the amplifier gain due to variations in voltage of the direct current source, and also due to changes in the operating characteristics of individual tubes.

Again, a feature of my invention is the provision of train carried train control apparatus incorporating an electron tube ampliiier wherein an additional capacitance-resistance biasing means is applied to the final stage tube and substantially uniform voltage is applied to the code following relay lnotivithstanding the received electroinotive force may vary over relatively wide limits. f

Another feature of roy-invention is the provision of a relatively simple, inexpensive and rugged amplifier for train carried train control apparatus. v

Other features, objects and advantages of my invention will appear as the specification progrosses.

The above features, objects and advantages of my invention I obtain by providing a two-stage amplifier using low voltage indirect heater type of electron tubes and whose plate and heater circuits are effectively excited when connected to a 32 volt source of vdirect current. The first stage tube is provided with separate and distinct filament (heater) `and plate-circuits connected in multiple across the 32 volt ysource of direct current. A resistor is included in the plate circuit adjacent the cathode of the tube, and this resistor is also included in the control grid circuit which is coupled to the receivingr circuit. The plate current flowing in this resistor provides a direct voltage which normally biases the first stage tube to function as a class A amplifier and provides an alternating bias voltage when coded energy is received which bias alternating voltage assures a substantially uniform amplifier gain over a relatively Wide variation of voltage of the direct current train carried source. Such inverse feed-back also minimizes the effects of variations in the operating characteristics of different tubes when a tube has to be changed,

Furthermore, the first stage tube is provided With an auxiliary 0r screen grid that is connected in a circuit including a resistor connected between the screen grid and the direct current source. `This special screen grid circuit serves v to control the flow of current in the control grid circuit and thereby governs the dampening of the receiving circuit to minimize code distortion When a rail current of large rdamping is interrupted at the end of each on code period and trolling apparatus. A stantV application to point out that the track oscillations tend to persist in the receiving circuit due to its resonant condition. Y

The second stage tube is normally biased to function as a class C amplifier and is provided with an additional capacitance-resistance `biasing unit whosev time constant isn such that the Voltage-'developed*across the capacitance isVre tained with little loss during the completecode' Vcycle and is added to the normal bias voltage to veiiect.substantially the same ainplier gain kfor large values as for normal values of the electromotive forcepicked up from the rails. I shall describeV one form of apparatusernaY bodying my invention and shall thenpoint out the novelfeatures thereof in claims.V p

In the accompanying drawing, Fig'. 1 is a diav grammatic View showing one form ofy apparatus embodying my invention when used with train,A

carried train control apparatus. Figs. -2 and 3 are diagrams illustrating operating characteristics of the apparatus of Fig. .l. Y

Referring to Fig/l, Vthe reference characters Inland Vlb designate the track rails of a railway.V

These rails Iva. and lb would befformed lby the usual insulated rail joints into consecutive track sections..` Codedv alternating current is supplied Y t end of cach trackV across the rails at e? section so that such currentA licws in the rails in series. TheY alternating current may be of any convenient-frequency and may be', for exn ample, of the order of 100 cycles per second. The trackway apparatus for supplying coded current to' the rails la and Eb isnot shown since it forms no part of mypresent invention and may be anyone of several well-known arrangements.

VFor example, the arrangement of such trackway d apparatus may bethat disclosed in Letters Patent ofthe United- States No. 2,250,191; granted lJuly 122, 1941 to'myself for Railway'traiic con- I* sumcient for the inrails Ia' and Ib are' supplied with alternating current'of ajpreselected frequency coded at difierent code rates and such current flows in the rails in series andvaries' in magnitude dueV to the diierentvalues of the rail impedance in the cir-' cuit as the train moves from the ent-ranceend to the exitfend of the track 'section and valso because ofchanges in ballast resistance and other conditions. n

Two inductors 'and ii aremounted on the train in advance of the leading pair'or wheels in'inductiverrelation to track rails Ia and lo, respectivelyi Inductors S and Il are connected in series inV a yreceiving circuit which also in cludes a'lter comprising transformer. Tl and condensers 5 and t. As here shown induotors 3 andi-i, condenser 5 and primary winding 'i' of transformer Ti are connected in series and ccndenser 5 is connected'across secondary winding 8 l'oftransformer Tl. vThis receiving circuit is Ytunedto resonancefat'the frequency of the Vrail current.V For example, when alternating'current Vof lOGcycles per second is used then this receiving circuit'is tuned tolresonance at 1GO cycles-per second.l It f oliows Vthatv an electromotivefor'ce is picked upby Vthe inductors Sand anda-cur' .respending"eiectromotiveA vforce .appears acrossA secondary winding 3 of transformer Ti, such pick-ed up electromotive force being of the 'free quency and codeiofV the railcurrent and vofa magnitude proportional tothe magnitude ofthe" rail current- :Secondary winding 8 and condenser Ii in multiple are connected tothe input ter- `respondingly longer interval because of the in- K Y creased charge built up on the condenser. Es-

pecially will this'be true at the lower code rates V.and the on code period is of a correspondingly 'longer interval to buildup the charge on the condenser.r In'other words, the oscillatory na- Y 'tureV ofthe receivingcircuit tends'to fill in the l valleys ofthe envelope oi the electrcmotive force appearing at the terminals of secondary. winding 8R01? transformer ECI when, large rail currents flow. Looking at Fig. 3, the full line envelope represents that offthe electromotive force across secondary winding. il .due to'anormal value of rail current, while the dottedjlines represent in outline the envelope of the electrorirotive force resulting when the rail current is of 'a large mag- A nitude. Under normal conditions the oscillations during the 01T code period are of such low value that they canbe neglected as far as their iniiu- `ence on the amplier.' However, the amplitude of the oscillations in the valleys' of'theenvelope when large rail currents flow may be substantially equal to the maximum amplitude Voifthe electromotive force during the on periodo-.nder normal rail current. VSuch lling in of the 'valleys of the envelope when large rail current flows causes code distortion and in extreme cases may result in unsatisfactoryoperation ofthe train carried apparatus.

The train carried amplifier comprisestwo stages which include Velectron tubes. VTi and VTZ, re-

spectively. Tubes VT! and VTi? may take dif- 40 ferent formsand may be indirect heater pentodes adaptable ofoperation on relatively low voltage such as32 volts. Looking at tube :VTi of the rst stage of the amplifier, its lament is connected across'the 'currentsource whose terminals are indicated `by the reierence Vcharacters B32 and-N32, and which maybe theterminals of the circuit which 'are separate and distinct andwliich are connected across the E32-N32 currentV source in multiple. Tube VTi yis provided with a control grid circuit including control grid It, condenser 5 and .secondary winding 8' of transformer Ti in multiple, resistor RI and Vcathode I3. An auxiliary or screen grid I5 of tube'VTI is included inv a circuit connected to the positive terminal B32 of the current source over a resistor R2., Control grid I4 is provided with a normal grid bias voltage equal tothe directvoltage drop acrossresistor R! due to the' normal plate current flowing therethrough. The parts arevso proportioned that the Y normal-bias voltage developed across resistorRi causes tube VT! `to function as a class A amplifier and hence wnenrvan alternating signaling electro.- motive force appears across secondary winding 8 ing 'current component'of the plate circuit curtube VTI is provided with a filament and a plate' of the receiving circuit a corresponding alternatalternating electromotive force vappears across secondary winding I6 of the coupling transformer T2. When .such alternating current component is created in .the plate circuit current, the direct voltage drop across resistor RI is reduced while an alternating voltage is created and which alternating voltage is substantially 180 degrees out of phase' with the signaling e'lectromotive force. The effective alternating voltage impressed on control grid I4 is then the difference between the signaling electromotive force derived from the receiving circuit and the biasing alternating voltage derived from resistor RI. This biasing, known as inverse feed back serves to minimize the ei'lects of variations in the tube characteristics upon the overall ampli-iler gain. For example. an increase of voltage of the E32-N32 current source would increase the normal plate current to increase the tube gain. Such increase of plate current develops largerralternating voltage across resistor RI and with a given signal voltage reduces the effective alternating voltage impressed upon control grid I4. However, the amplifier gain of tube VTI would not be lowered greatly by such decrease in the impressed alternating voltage because of the higher gain at which the tube is operated. `I have found that such inverse ieed back causes the tube to operate at substantially the same ampliergain with the voltage of the E32- N32 current source varying'fro-m a minimum of 26 volts to a maximum of 40 volts. Also the amplifier gain is not aected materially by variations in operating characteristics of different tubes due to manufacturing variations.

Screen grid I5 and itsY circuit includingv resistor R2 serve to reduce the effects ofthe oscillatory condition of the receiving circuit and avoid code distortion. When the rail currentis relatively large, control grid I4 is driven positive by the positive half cycles of the signaling electromotive force and hence grid current flows and acts as a load across the receiving circuit filter. The presence oi the load on the receiving circuit serves to damp the oscillations and they persist a shorter interval than would be the case if there was no load. When the control grid i4 is driven positive by the incoming signaling electrornotive force, the plate't'o cathode voltage is at a minimum value. The screen grid current tends to be a maximum, but due to the voltage drop in resistorvRS! the screen grid voltage is reduced during' this interval. With the lowering of plate and screen grid voltages, control grid draws more current than is normally the case and oiers more of a load on the nlter of the receiving circuit. This increase in the load on the receiving circuit causes greater damping of the oscillations and lessensy the code distortion. That is, the screen grid circuit serves to increase the damping of the receiving circuit and minimize code distortion caused by the oscillatory condition of receiving circuit at the higher values of the rail current.

The second stage tube VT2 is providedwith a filament circuit for heating its filament I'! and with a plate circuit both of which include a resister E8, as will be readily understood by an inspection of Fig. 1. Cathode 2I of the second stage tube V132 is connected to the negative terminal of filament il. while screen grid 2 is connected 'to the positive terminal of filament Il.

Secondary winding I6 of coupling transformer T2 is connected across control grid 23 and cathode 2| ofthe second stage tube VT2, the heater circuit resistor I8 being also included in this control grid circuit. The parts are so proportioned that s the voltage drop across resistor I8 due to the heater circuit current flowing therein biases the tube VT2 to substantially zero plate current and thereby causes tube VT2 to function as va class C amplifier'.

An additionalrbiasing unit comprising a condenser C and a resistor RL are connected to the control grid circuit of tube VT2 to provide an additional biasing voltage for the tube, condenser C being connected in series with the control grid 23 and resistor RL being connected as a grid leak resistor. When the electromotive force appearing across secondary winding I6 of transformer T2 is that created by a normal value of rail current, grid 23 is not driven positive in potential with respect to cathode 2I and no grid current flows. However, grid 23 is driven in the positive direction during the positive half cycles of the electrornotive force appearing across secondary winding I5 and plate current flows, the plate current having a predetermined average value to which it builds up during each on code period and from which it decays during each ofi code period. When the signaling electromotive force appearing across secondary winding I6 of transformer T2 is large due to rail current of large magnitude, grid 23 is driven positive in potential with respect to cathode 2I during the higher values of each positive half cycle of the signaling electromotive force, and grid current ows and condenser C is charged. The time constantof the unit cornprising condenser C and resistor RL is made such that the potential developed across condenser C during an on code period is retained with little loss during the next oil code period, with the result the bias voltage of the C-RL unit is added to the normal bias voltage derived from resistor I8. The resultant bias voltage tends to reduce the plate current and a nearly uniform change in the average value of the plate current takes place over a relatively wide variation in the magnitude of the rail current.

Referring to Fig. 2, the'plate current of the second stage tube VT2 is shown as a function of the rail current. When `a normal value of rail current flows, the alternating voltage applied to control grid 23 of tube V .U2 is represented by the two graphs just below the horizontal axis', that is, the alternating voltage for two code cycles is illustrated. Under such values of the applied voltage, the changein the average value of the plate current for tube VT2 is represented by In, such change being due to the bias voltage derived from resistor I3 alone because at such value of rail current the applied voltage is not sufficient to drive grid 23 positive potential with respect to cathode 2i. Rail current ci a large magnitude tends to create an alternating voltage across secondary winding i5 illustrated by the two center graphs oi Fig. 2, that is, two code cycles are illustrated'. The maXi-' mum value of the voltage is increased. but due to the possible code distortion the minimum valueto which the voltage may fall dur the' oi code periods may be relatively la and hence the change of 'the plate current may be that illustrated by Im of 2. which. change may be less than that efected by rail current `of normal value.` Under conditions oi large rail current the voltage applied to tube` VT2 is such thatgrid 23 is maderpositve duri the higher values of the positive half cycle andA grid current flows to charge condenser C with l primary Winding theresult that unit C-RL serves to provide anl additional'gr'id bias voltage. Due to this additional grid bias voltage .effected through ltheun-it 'Q -RL, the applied voltage to tube VT2 corresponds toVY that illustrated by the vtwo lower `graphs of Fig. 2, that is, two codev cycles are illustrated. ,Under this condition, the change in the average -value of the plate circuitjcurrent remains substantially the same as that effected in response .to the rail current of normal value.

A code following relay CF of therusual type is connected to secondary, ,winding 2,5 Vof output transformer T3 whose primary Winding I9 is interposed in the plate Vcircuit of the second stage tube V'IZ and across which primary winding a n condenser 22 is preferably connected. Relay CF is operated in response to `thevoltage induced in secondary Winding 25, due to the changes in the average valuerof the plate current flowing in I9, the arrangement Vbeing such that relay CF is energized at a polarity to operate the relay to close its normal polar contact 2l When current builds up in the plate circuit of tube VT2 a-nd is energized at a polarity to operatethe relay to close reverse polar contact 28 rwhen the plate current dies away. Code following relay CF governs Athe supply ci direct 1 current to the primary-Winding E@ ci a decoding transformer DT,v current being alternately supplied to the two portions of primary winding V2li over normal contact 27 and reverse contact A28, respectively. rEhe alternating electromotive force induced in secondary Winding 29 of dccoding transformer DT is applied to a decoding unit shown conventionally'at DU and which decoding unit may be of the Well-known'forln of tuned circuits for selectively controlling three relays A, R and L according to the code Vrate at which the relay is operated. For example, when the usual code rates of 180, 12'3 and 75 are provided for the rail current, then relays A and L are picked up and relay R is released for the 180 code rate, relays R. and L are picked upv and relay A is released for the 120 coderate,

and relay L is picked up and relays A and R are released for the '75v code rate. When relay CF is inactive,.then all three relays A, R and L vare released. Relays-A, R and `l'.. are used to govern the operating'circuits of a traincontrolling device, such as al cab signal CS, the operating circuits of Which cab signal are arranged inthe usual Well-known manner, ias will be readily understood by an inspection of Fig.V l.`

Train carried'train control apparatus here disclosed has the advantagesthat it is simple,inexpensive and rugged, and is excited by a single 32 volt source of direct current. The electrornctive force picked up by the usual train carried receiving circuit when a predetermined value of railA current ows is amplified at relatively high gain without code distortion to apply a predetermined voltage to the code follov/'ingrelayV for operating that relay at a ratecorresponding to the code rate of the rail current. YVariations in amplification Ygain Vof the'rst stage tube caused by increase in voltage Vof the direct current source of supply is compensated by the inverse -ieedbackV provided for the irst stage tube; i' Codedistortion at the higher values of the rail current due to the oscillatory condition'oithe receiving s Vcircuit is minimized by the control of the dampingfof` the receiving `circuit through the means of a screen grid circuitr including a resistor of` aV predetermined Value. YSubstantially equal changes in the plate current of the nal stage` f plate circuit current.

tube are eiected by the additional capacitanceresistance biasing unit which serves to increase the negative grid bias of the iinal stage tube when rail current of larger magnitudeprevails.

Although I have herein shown and described only one form of railway traic controlling apparatus embodying my invention, it is understood that various changes` and Vmodifications i may be made therein Within the scope of the appended claims Without departing from the spirit and scope of my invention.

Having thus described my invention, what I claimis: y

l. In controlling apparatus for use with alternating current coded at a preselected code `rate and supplied to a receiving circuit tuned to reonance at the frequency of said alternating current, theV combination comprising; an electron tube having a plate, a cathode, aV control grid and a screen grid; aV plate circuit for said tube including a source of direct current, a control grid circuit connected across said control. grid and cathodejand coupled to said receiving circuit to cause in the plate circuit current an alternating current component of a code corresponding to that of the alternating current, another grid circuit including a resistor connected between said screen grid and said direct Vcurrent source independent of the other circuits of the tube to control the damping of said receiving circuit for minimizing'code distortion due to the resonant condition-of the receiving circuit, and a code following relay coupled to `said plate circuit and governed by said coding of the alternating current component of the plate circuit current for operation of the relay at said code rate.

2. In controlling apparatus for use with coded alternating current that is supplied to a receiving circuit tuned to resonance at the frequency of said alternating current, the combination comprising; an electron tube having a plate, a cathode, a control grid and a screen grid; a plate circuit for said tube including a source of direct current and a resistor disposed adjacent said cathode, a control grid circuit for said tube cou-` pled to said receiving circuit and including said plate circuit resistor to provide a control grid bias voltage derived solely by the voltage dropV across the resistor due to the plate circuit current for effecting a substantially uniform amplifying gain for the tube over a relativelylarge variation in the voltage of said direct current source, another circuit including Vanother resistor connected between said screen grid and said direct current source to control the damping of said receiving circuit for minimizing code distortion due to the resonant condition of the receiving circuit, and a code following relay (coupled to said plate circuitV and energized due to code rate variations of the plate circuit current caused` by the coded alternating current component of the 3. In controlling apparatus for use with coded alternating current Which is supplied to a receiv- V said alternating current, the combination com-` ing circuit tuned to resonance at the frequency of prising; an `electron tube having a a platera cathode,` a control grid and another grid;Y

a source of direct current-separate and independ- Y ent filament and-plate circuits for said tube connected in'fmultiple across said direct current source, a iirst resistor interposedin said plate circuit adjacent said cathode, a control Vgrid lcircuit for' said tube including said'first resistor and coupled to saidreceiving circuit to amplify in the plate circuit current the coded current supplie-:l to said receiving circuit, another grid circuit for the tube independent of said filament circuit and including a second resistor connected between s id other grid and the positive terminal of said direct current source, said plate circuit current fiowing in said first resistor to create a direct and alternating bias voltage to provide a substantially uniform amplifying gain for said tube, said other grid circuit current flowing in said second resistor to control the damping of said receiving circuit to minimize code distortion when the coded current is of relatively large magnitude, and a code following relay coupled to said plate circuit energized due to the code rate variations of the plate circuit current caused by the coded alternating current component of, the plate circuit current.

4. In controlling apparatus for use with a coded alternating current which is supplied to a receiving circuit tuned to resonance at the frequency of said alternating current, the combination comprising; an electron tube having a filament, a plate, a cathode, a control grid and a screen grid; a source of direct current of a preselected voltage, separate and distinct filament and plate circuits for said tube connected in multiple across said direct current source, a first resistor interposed in said plate circuit adjacent said cathode, a control grid circuit for said tube including said first resistor and coupled to said receiving circuit to cause in the plate circuit an alternating current component of a code corresponding to that of said alternating current, a screen grid circuit independent of said filament circuit and including a second resistor connected between said screen grid and the positive terminal of said direct current source, said control grid provided with a direct and an alternating bias voltage derived solely by the plate circuit current flow in said first resistor to maintain a substantially uniform amplifying gain for the tube when the voltage of said direct current source varies from said preselected voltage, said screen grid circuit to control the damping of the alternating voltage applied to said control grid to minimize code distortion due to the resonant condition of said receiving circuit when the coded current is of large magnitude, and a code following relay coupled to said plate circuit and energized due to the coded alternating current component thus caused in the plate circuit.

5. In controlling apparatus for use with a transmitting circuit supplied with coded alternating current and a receiving circuit in inductive relation to said transmitting circuit, the combination comprising; a two stage amplifier each of which stages includes an electron tube, a source of direct current, separate and independent filament and plate circuits for the first stage tube connected in multiple across said direct current source, a control grid circuit for said first stage tube coupled to said receiving circuit, a first resistor common to the plate and control grid circuits of the first stage tube to provide a grid bias voltage due solely to the Gil plate circuit current flowing in said first resistor governing the amplifying gain of the rst tube, a plate and a filament circ it econd stage tube connected to saitl source, a control grid circuit i r stage tube coupled to the plate c cuit of the first stage tube; a second resistor camino-n to the filament, plate and control grid circuits of the seccnd stage tube to provide a negative grid bia-s Voltage that normally effects zero plate current; an additional biasing unit consisting of a condenser and a resistor interposed in the control grid circuit of the second stage tube and provided with a time constant such that the voltage developed across the condenser is retained during a complete code cycle of said coded alternating current to effect a substantially uniform change of the second stage tube plate circuit current over a relatively wide range of values of said coded current, and an electromagnetic relay coupled to the second stage tube plate circuit and energized due to the change in the current flowing therein.

6. In controlling apparatus for use with a transmitting circuit supplied with coded alternating current and a receiving circuit in inductive relation to said transmitting circuit, the combination comprising; a two stage amplifier each of which stages includes an electron tube, said first stage tube having a screen grid as well as a control grid, a source of direct current, separate and independent filament and plate circuits for the first stage tube connected in multiple across said direct current source, a control grid circuit for the first stage tube coupled to said receiving circuit, a first resistor common to the plateand control grid circuits of the first stage tube to provide a grid bias voltage due solely to plate current fiowing in said first resistor to maintain a substantially uniform amplifying gain for the first stage tube over a relatively large variation of voltage of said direct current source, a screen grid circuit independent of said filament circuit and including a second resistor connected between said screen grid and said direct current source to control the damping of said receiving circuit and reduce code distortion caused when said coded alternating current is of large magnitude, a plate and a filament circuit for said second stage tube connected across said direct current source, a controlfgrid circuit for said second stage tube coupled to the first stage tube plate circuit; a third resistor common to the filament, plate and grid circuits of the second stage tube to normally bias said second stage tube to zero plate current; an additional biasing unit consisting of a condenser and a resistor interposed in the second stage tube grid circuit to effect an additional grid bias voltage and maintain substantially the same change in the second stage tube plate circuit current when the coded alternating current is of large magnitude as when the coded current to the second stage tube plate circuit governed yby the change in circuit flowing therein.

RALPH K. CROOKS. 

